1. Field of the Invention
This invention relates to a dispersion the liquid crystal electro-optical device having a liquid crystal--resin complex of a primer resin and a liquid crystal material or a liquid crystal--resin complex in which resin is dispersed in liquid crystal material.
2. Description of Related Art
TN type or STN type electro-optical device using a nematic liquid crystal or the like has been well known and practically used as a liquid crystal electro-optical device. Recently, a device using ferroelectric liquid crystal is also known. In these electro-optical liquid crystal devices, basically, liquid crystal compound is kept in between a first substrate having an electrode and a lead thereon, and a second substrate having an electrode and a lead thereon. Through the electrodes on the substrate, an electric field is applied to the liquid crystal compound, and a state of the liquid crystal molecules is varied by anisotropy of a dielectric constant of a liquid crystal material itself or spontaneous polarization when the liquid crystal is formed of ferroelectric liquid crystal. Consequently, an electro-optical effect which is induced by the variation of the state of liquid crystal molecules is utilized.
In a TN or STN type liquid crystal electro-optical device, liquid crystal molecules are oriented along a rubbing direction on the contact surface between a liquid crystal layer and each of the substrates by a restricting force which is induced by a rubbing carried out for an orientation treatment. The rubbing directions on the upper and lower substrates are deviated from each other by an angle of 90.degree. or 200.degree.-290.degree.. The liquid crystal molecules at the center portion of the liquid crystal layer are aligned spirally between the upper and lower molecules which are located with angular deviation from 90.degree. to 200.degree.-29O.degree. so that an energy is minimum. In this case, chiral material is mixed into the liquid crystal material in the STN type if an occasion demands.
All of these device have a polarizer and requires the liquid crystal molecules to be regularly oriented along a fixed direction in a liquid crystal electro-optical device. This orientation treatment is carried out by rubbing an orientation film (an organic film in a usual case) in a fixed direction with cotton or velvet cloth. If no orientation treatment is conducted, the liquid crystal molecules would not be oriented in the fixed direction, and thus the electro-optical effect of liquid crystal can not be utilized. Thus, the device is designed in a vessel structure in which liquid crystal material is kept by a pair of substrates, and the liquid crystal is injected into the vessel and oriented to utilize the optic effect of the injected liquid crystal.
On the other hand, there has been known a dispersion type liquid crystal which requires no polarizer and no orientation treatment and provides a bright and high-contrast screen. This dispersion type liquid crystal is constructed such that transparent solid-state polymer keeps liquid crystal material in a granular or sponge form to form an electro-optical modulating layer. Conversely, another type is constructed such that a solid-state polymer is dispersed in liquid crystal material and the liquid crystal material is oriented uniformly and randomly. As a method of producing this liquid crystal device has been known a method in which encapsulized liquid crystal material is dispersed in polymer, and the polymer is formed in the form of a film or in the form of a thin film on a substrate. Here, Arabic rubber, polyvinyl alcohol, gelatin or the like is used as capsulizing material.
For example, liquid crystal molecules capsulized by polyvinyl alcohol are oriented under electric field such that the long axis thereof is parallel to the electric field if the liquid crystal molecules have positive dielectric anisotropy in a thin film, and transparency appears when refractive index of polymer is equal to refractive index of liquid crystal. On the other hand, since under no electric fields the liquid crystal molecules do not orient in a specific direction, but orient in various directions, a difference between refractive index of liquid crystal and refractive index of polymer becomes large, so that incident light is scattered and light transmission is prevented, and an opaque state appears, Various informations are presented by utilizing this difference between the transparent state and the opaque state. In addition to the encapsulated liquid crystal, a type that liquid crystal material is dispersed in epoxy resin, a type that liquid crystal and a photocuring resin are mixed with each other and light is irradiated to photocure the resin and utilize a phase separation between the liquid crystal and the resin, and a type that liquid crystal is absorbed into three-dimensionally linked polymers, have been known as a dispersion type of liquid crystal. In this invention, these are commonly referred to as "dispersion type liquid crystal".
In this dispersion type liquid crystal electro-optical device, light transmittance of the liquid crystal electro-optical device is markedly high in comparison with the conventional TN and STN type electro-optical device because no polarizer is used. Specifically, the permeability of one polarizer is about 50%, and for an active matrix using these polarizers in combination, only about 1% of light can transmit. The permeability of the STN type is about 20%. Therefore, in these cases, an effort for heightening the brightness of a screen by increasing intensity of illumination of back light has been made. On the other hand, over 50% of light transmits in the dispersion type liquid crystal electro-optical device. This is a superiority of the dispersion type of liquid crystal owing to no use of polarizer.
As mentioned above, the dispersion type liquid crystal is used between the transparent state and the opaque state, and it has been ordinarily researched and developed as being used for the transmission type liquid crystal electro-optical device because amount of light transmitting through a liquid crystal electro-optical device is large. Of the transparent types, it has been developed particularly as being used for a projection type liquid crystal electro-optical device. This projection type liquid crystal electro-optical device is so constructed that a liquid crystal electro-optical device panel is placed in a light path of light emitted from a light source and the light transmitted through the panel is projected on a wall surface through a slit having a fixed angle. Liquid crystal molecules in the panel orient in various directions in a low electric field region below a threshold value where the liquid crystal dose not respond to an applied voltage, and thus the panel is in an opaque state.
The light incident to the panel at this time is scattered after transmission through the panel, and the light path of the incident light is broadened. Therefore, the scattered light is cut off by the slit which is placed at a next stage, so that the light hardly reaches the wall surface and a dark state is obtained. On the other hand, when the liquid crystal responds to the applied voltage and liquid crystal molecules orient in parallel to the electric field, the incident light transmits straightly through the panel without being scattered and thus a light state of high brightness is obtained on the wall surface.
In these dispersion types of liquid crystal electro-optical devices, since a display contrast is dependent on a degree of scattering of the incident light which is based on variation of the orientation state of the liquid crystal material, it is required to keep the liquid crystal material in a fine-droplet state in the device. The dimension of the droplet is set to 10 microns at the maximum and 0.05 micron at the minimum, and is set to 0.3-3 microns usually.
In the dispersion type liquid crystal electro-optical device, the scattering and straight transmission of light due to this fine droplet are utilized, so that it is required to form droplets having uniform size over the liquid crystal electro-optical device. However, it has been very difficult to uniformly form such fine droplets of liquid crystal over the substrate of the liquid crystal electro-optical device.
That is, as a method of forming fine droplets of liquid crystal has been mainly utilized a phase separation method that liquid crystal material and resin material are mixed and then the resin material is cured, or a method that liquid crystal material and resin material are mixed and then is subjected to a capsulization treatment through reaction in liquid phase or the like. However, both of the methods depend on the curing characteristics of the resin material and the like, and thus it is difficult to form the droplets in uniform size.